[ty] Distribute type[] over unions (#22115)

## Summary

Closes https://github.com/astral-sh/ty/issues/2121.

crates/ty_python_semantic/resources/mdtest/implicit_type_aliases.md

@@ -1179,6 +1179,34 @@ def _(
     reveal_type(subclass_of_p)  # revealed: type[P]
 ```
 
+Using `type[]` with a union type alias distributes the `type[]` over the union elements:
+
+```py
+from typing import Union
+
+class C: ...
+class D: ...
+
+UnionAlias1 = C | D
+UnionAlias2 = Union[C, D]
+
+SubclassOfUnionAlias1 = type[UnionAlias1]
+SubclassOfUnionAlias2 = type[UnionAlias2]
+
+reveal_type(SubclassOfUnionAlias1)  # revealed: <special-form 'type[C | D]'>
+reveal_type(SubclassOfUnionAlias2)  # revealed: <special-form 'type[C | D]'>
+
+def _(
+    subclass_of_union_alias1: SubclassOfUnionAlias1,
+    subclass_of_union_alias2: SubclassOfUnionAlias2,
+):
+    reveal_type(subclass_of_union_alias1)  # revealed: type[C] | type[D]
+    reveal_type(subclass_of_union_alias1())  # revealed: C | D
+
+    reveal_type(subclass_of_union_alias2)  # revealed: type[C] | type[D]
+    reveal_type(subclass_of_union_alias2())  # revealed: C | D
+```
+
 Invalid uses result in diagnostics:
 
 ```py

crates/ty_python_semantic/resources/mdtest/type_of/generics.md

@@ -71,6 +71,29 @@ reveal_type(constrained(str))  # revealed: str
 constrained(A)
 ```
 
+`type[T]` with a union upper bound `T: A | B` represents the metatype of a type variable `T` where
+`T` can be solved to any subtype of `A` or any subtype of `B`. It behaves similarly to a type
+variable that can be solved to any subclass of `A` or any subclass of `B`. Since all classes are
+instances of `type`, attributes on instances of `type` like `__name__` and `__qualname__` should
+still be accessible:
+
+```py
+class Replace: ...
+class Multiply: ...
+
+def union_bound[T: Replace | Multiply](x: type[T]) -> T:
+    reveal_type(x)  # revealed: type[T@union_bound]
+    # All classes have __name__ and __qualname__ from type's metaclass
+    reveal_type(x.__name__)  # revealed: str
+    reveal_type(x.__qualname__)  # revealed: str
+    reveal_type(x())  # revealed: T@union_bound
+
+    return x()
+
+reveal_type(union_bound(Replace))  # revealed: Replace
+reveal_type(union_bound(Multiply))  # revealed: Multiply
+```
+
 ## Union
 
 ```py